1. Technical Field
The present invention relates to a method and device for pressure indication. In particular, the invention relates to a method and device for indicating an air pressure of a cuff of a laryngeal mask or other airway device.
2. Description of the Related Art
In 1988, Dr. Archie Brain invented a new airway device, called the laryngeal mask, for delivering anesthetic gases and oxygen to an unconscious patient during an operation. Prior to this, patients were commonly anaesthetized using an Endotrachial Tube running through the vocal cords of the patient into the trachea. Alternatively, a face mask connected to a gas source was held over the patient's nose and mouth.
In use, the laryngeal mask is inserted into the pharangeal space (throat) deflated, and when correct positioning is observed, an inflatable cuff around the outside of the mask is inflated with air using a syringe. The syringe is inserted into an end of a valve which is connected to the cuff by a small tube, such that air passed through the valve from the syringe is used to inflate the cuff. There are presently eight different sizes of the laryngeal mask available, and while all require different volumes of air to inflate the cuff, the maximum recommended intra cuff pressure is 60 cm H2O.
The Laryngeal Mask is now the preferred choice of anesthetists in many countries, and its use continues to grow. The greater prevalence in use of the laryngeal mask has brought certain possible dangers to light. Due to human errors and the possible diffusion of nitrous oxide into the silicone cuff, the cuff may be excessively inflated. Such excessive inflation of the cuff has the potential to damage nerves and tissues around the hypopharynx, and this potential danger has been the subject of scientific papers in anesthesia journals.
In order to prevent over-inflation of the cuff, it is desirable to check the intra cuff pressure when the laryngeal mask is in place. Currently, the means for checking the air pressure of the cuff include a small inflatable bulb in fluid communication with the cuff inflation tube. To get an indication of the cuff pressure, medical personnel squeeze the bulb under slight pressure from their figures to thus subjectively judge the intra cuff pressure. Alternatively, a manometer may be connected to the cuff inflation valve in order to obtain an accurate pressure measurement. Manometers are, however, relatively expensive and somewhat bulky and can be inconvenient to connect to the cuff inflation valve as the valve is usually close to the patient's mouth.
Similar problems can occur in other airway devices having an inflatable cuff, such as endotrachial tubes, for example.